The invention generally is directed to methods and apparatus for measuring the presence and/or concentration of a gas, e.g., oxygen, by exploiting the paramagnetic properties of the gas and by employing at least one member that comprises a substance having diamagnetic properties on which a force is exerted, given the presence of the gas, due to the paramagnetic properties of the gas. More specifically, the invention is directed to paramagnetic gas/oxygen measuring devices/instruments.
The acquisition and interpretation of measurements of gases such as oxygen concentrations are necessary in various situations, for example, process control, operating analysis, environmental protection, as well as in research and development. Modern gas analyzers which are employed to obtain oxygen measurements generally are computer assisted instruments with extremely compact structures.
One such gas/oxygen analyzer is disclosed in a brochure provided by Leybold AG bearing the designation "Oxynos 100" and the number 43-520.01.
Another paramagnetic measuring instrument is disclosed in U.S. Pat. No. 4,772,848 the teachings of which are fully incorporated herein.
Further, various paramagnetic measuring devices having mechanical gas/oxygen measuring modules are known that output a deflection due to the presence of paramagnetic gases, the deflection in turn being transduced into an electrical signal related thereto.
However, the transverse sensitivity (i.e., an unwanted measuring sensitivity of a measuring module to a gas constituent that one does not want to measure) in the prior art devices can be greater than predicted in theory. Non-magnetic gases and particles as well as aerosols can have a considerable influence on the measurement. These influences are undesirable because they introduce inaccuracies in the measurement.
Prior art devices are also limited in that they are sensitive only down to a resolution of two percent oxygen by volume. Below this resolution of two volume percent oxygen, negative influences of water content of a damp gas are so great that fast precise measurements are not possible.
Further, chronologically slow transient effects can appear, these effects being capable of causing unwanted distortion. These transient effects include adsorption and absorption of water particles or water films that produce inaccuracies in the resulting measurements.
Attempts have been made to overcome the above-described limitations by thermostatically controlling the measuring cells. However, thermostat control of measuring cells has provided only a relatively slight improvement. Modern oxygen analyzers must be able to suppress transverse sensitivity to a greater degree to meet future demands.